The modern era has seen science and technology used for large-scale destruction, with increasingly deadly weapons developed and used in actual battles, starting with tanks, bombers, and poison gases(chemical weapons)in World War I, and moving on to biological weapons in the 1930s and nuclear weapons in World War II. During the Cold War, the U.S. and the Soviet Union entered an arms race and deployed massive quantities of nuclear weapons under the theory of "deterrence"-the notion that fear of mutual annihilation would prevent war. After the great losses it suffered in the Vietnam War,America has been pursuing the development of easy-to-use miniature nuclear arms and other hi-tech weapons to minimize American casualties. Today, military satellites and information technology are being used to make weapons increasingly accurate and powerful, with America maintaining an overwhelming lead in improving and deploying advanced weaponry.